Method of operating an electrically assisted turbocharger and a boosting device

ABSTRACT

A method of operating a turbocharger is provided, wherein the turbocharger comprises a compressor for compressing inlet air to be supplied to an internal combustion engine and an exhaust gas turbine for driving said compressor. The turbocharger further comprises an electric motor for driving said compressor operable by an electric supply system including an alternator and an electric energy storage device. A connection between said alternator and said electric energy storage device is disconnectable by a switch. According to the present invention, the method comprises the following steps: 
     detecting a transient condition, wherein said internal combustion engine is required to be accelerated; 
     supplying electric energy to said electric motor only from said electric energy storage device at the beginning of said transient condition until a predetermined state is reached; 
     supplying electric energy to said electric motor from the electric supply system after said predetermined state is reached.

The present invention relates to a turbocharger system and a boostingsystem and, in particular, to a method of operating a turbocharger and aboosting device.

It is known from the state of the art to provide an internal combustionengine for vehicles with a turbocharger system so as to increase theoutput of said internal combustion engine and in order to reduce thefuel consumption while maintaining a sufficient performance of thevehicle. Such a known turbocharger system employs a compressor driven bya turbine which, in turn, is driven by exhaust gas discharged from theinternal combustion engine. The compressor increases the pressure ofinlet air supplied to combustion chambers of the internal combustionengine. Thereby, the power output of the internal combustion engine andan overall efficiency are increased.

Furthermore, it is known from the state of the art to provide aninternal combustion engine with a boosting device which comprises acompressor which is driven by e.g. an electric motor.

In such a turbocharger or boosting system, a control is necessary inorder to adapt the operational condition of the turbocharger system tothose of the internal combustion engine.

It is the object of the present invention to provide a method ofoperating a turbocharger and a boosting device which increases theperformance and functionalities of the overall system of the internalcombustion engine and which improves the response behaviour thereof.

The object is solved by a method having the combination of the featuresof claim 1 or claim 12. Further advantageous developments are defined inthe dependent claims.

According to a first aspect of the present invention, a method ofoperating a turbocharger is provided, wherein the turbocharger comprisesa compressor for compressing inlet air to be supplied to an internalcombustion engine and an exhaust gas turbine for driving saidcompressor. The turbocharger further comprises an electric motor fordriving said compressor operable by an electric supply system includingan alternator and an electric energy storage device. A connectionbetween said alternator and said electric energy storage device isdisconnectable. According to the present invention, the method comprisesthe following steps:

detecting a transient condition, wherein said internal combustion engineis required to be accelerated;

supplying electric energy to said electric motor only from said electricenergy storage device at the beginning of said transient condition untila predetermined state is reached;

supplying electric energy to said electric motor from the electricsupply system after said predetermined state is reached.

According to the present invention, the electric energy for driving saidelectric motor is exclusively supplied from said electric energy storagedevice at the beginning of said transient condition and not from thealternator in that case where the connection between the alternator andthe energy storage device is disconnected. Thereby, an increasing loadapplied to the alternator is prevented which, in turn, effects that themechanical load required for driving said alternator is not increaseddue to the electric energy supplied to said electric motor.

According to the basic concept of the present invention, the responsebehaviour of the turbocharger is improved due to an assisting powerderived from the electric motor for accelerating the turbocharger inthat case where the acceleration of the turbocharger is required. Theimprovement of the response behaviour of the turbocharger effects animprovement of the overall system operability including the internalcombustion engine and the turbocharger. By disconnecting the alternatorfrom the energy storage device such as the battery so as to prohibit anincreased load to be applied to the alternator, since the electricenergy is exclusively supplied from said electric energy storage deviceto said electric motor, the vehicle performance is improved, by avoidingparasitic drag torque due to alternator during vehicle acceleration.

Preferably, said connection between said electric energy storage deviceand said alternator is disconnected from the beginning of the transientcondition until the predetermined state is reached. In a transientcondition, said internal combustion engine is required to beaccelerated. Therefore, an increased inlet air amount is to be suppliedto said internal combustion engine from said turbocharger. This resultsin the requirement to accelerate the rotational speed of theturbocharger in a short period of time. Such an acceleration in a shortperiod of time can be assisted by the electric motor by supplyingelectric energy to said electric motor. However, at the beginning of thetransient condition a high quantity of electric power is required toaccelerate the turbocharger. Disconnecting the connection between saidelectric energy storage device and said alternator from the beginning ofthe transient condition effects that the electric power is not derivedfrom the alternator but from the electric energy storage device only.The disconnection of said connection is maintained until thepredetermined state is reached so as to prevent a state of charge ofsaid electric energy storage device to fall below a minimum state ofcharge or to prevent an overload with respect to a current from thebattery which is only allowable over a short period of time.

Preferably, said predetermined state is reached after the elapse of apredetermined time period from the beginning of the transient condition.This predetermined time period can be set in accordance to the propertyof said electric energy storage device. Any breaking or overload of saidelectric energy storage device can be prevented in a simple manner.

Preferably, said predetermined time period is substantially 1 second. Inthe usual operation of the internal combustion engine, the transientcondition lasts for about 1 second. Furthermore, the electric powersupplied from said electric energy storage device can be maintained oversuch a period without causing any damage at the electric energy storagedevice. However, the period of time can be set to any other appropriatepredetermined period as long as the effects of the present invention areachieved. Also, the predetermined time period can be set variabledepending on other conditions or values.

Preferably, a rotational speed of said internal combustion engine isdetected and said predetermined state is a predetermined rotationalspeed of said internal combustion engine. That is, the transientcondition is assumed to be terminated after a predetermined rotationalspeed of said internal combustion has been reached. Furthermore, thealternator is able to generate a sufficient amount of electric energy tomeet the requirements of the power to be supplied to the electric motor.Preferably, said alternator is driven by said internal combustion engineand generates electric energy for the electric supply system.Furthermore, said alternator is capable of charging said electric energystorage device when said connection between said electric energy storagedevice and said alternator is enabled.

Preferably, a state of charge of said energy storage device is monitoredand said connection between said electric energy storage device and saidalternator is reconnected in case that said state of charge is smallerthan a predetermined state of charge. By reconnecting the connectionbetween said electric energy storage device and said alternator in casethat said state of charge is smaller than a predetermined state ofcharge, the damage of said electric energy storage device can beprevented which results from the fact that the state of charge issmaller than a critical lower limit. Furthermore, a failure of theoperation of said electric motor for assisting said turbocharger isprevented.

Preferably, a power output capacity of said alternator is monitored andsaid connection between said electric energy storage device and saidalternator is reconnected when said power output capacity of saidalternator is higher than the demand of said electric motor andremaining consumer loads derived from the electric power supply system.By reconnecting said connection when the power output capacity of saidalternator is higher than a predetermined value any failure in supplyingelectric energy to said electric motor can be prevented. Furthermore,the power output of said alternator indicates a condition wheresupplying the electric energy exclusively from said electric energystorage device is no longer necessary.

Preferably, said connection between said electric energy storage deviceand said alternator is connectable and disconnectable by a switch. Aswitch can provide open or closed states so as to enable the connectionand disconnection between said electric energy storage device and saidalternator. Furthermore, such a switch is capable of being controlled bycontrol signals transmitted from a control circuit.

Preferably, said compressor and/or said exhaust gas turbine comprises avariable nozzle wherein said nozzle is adjusted based on the state ofsaid connection between said electric energy storage device and saidalternator. The state of said connection indicates the transientcondition or at least a condition where the turbocharger is to beaccelerated, and the adjusting of the variable nozzle to the presentstate enhances the efficiency and performance of the turbocharger andthe overall system.

According to a second aspect of the present invention, a method ofoperating a boosting device is provided wherein the boosting devicecomprises a compressor for compressing inlet air to be supplied to aninternal combustion engine and an electric motor for driving saidcompressor operable by an electric supply system including an alternatorand an electric energy storage device, wherein a connection between saidalternator and said electric energy storage device is disconnectable.Furthermore, said method comprises the following steps: detecting atransient condition wherein said internal combustion engine is requiredto be accelerated, supplying electric energy to said electric motor onlyfrom said electric energy storage device at the beginning of saidtransient condition until a predetermined state is reached, supplyingelectric energy to said electric motor from the electric supply systemafter said predetermined state is reached.

According to the second aspect of the present invention, the boostingdevice is an electrically driven compressor which can be usedstand-alone or in combination with an additional exhaust gas driventurbocharger. With the second aspect of the present invention, the sameeffects can be achieved as with the first aspect of the presentinvention. In particular, the method of operating the electric boostingdevice provides the same advantages irrespective of the provision of theexhaust gas turbine for driving a turbocharger or the provision of thecompressor only which is driven by the electric motor.

Preferably, said boosting device further comprises an exhaust gasturbine for driving said compressor. Thereby, the boosting device isusable as a turbocharger and the advantage of a turbocharger is providedin the boosting system.

Each of the above-explained preferable forms of the method of operatinga turbocharger according to the first aspect of the present inventionare applicable to the method of operating the boosting device accordingto the second aspect. Thereby, the same effects and advantages areachieved with the first aspect and the second aspect of the presentinvention.

In the following, preferred embodiments and further technical solutionsare described in detail with reference to the accompanying drawings.

FIG. 1 shows a schematic illustration of the overall system comprisingthe internal combustion engine, the turbocharger and the associatedcontrol system for controlling the same according to the presentinvention.

FIG. 2 shows a schematic illustration of the electric supply system towhich the method according to the present invention is applicable.

FIG. 3 is a flow chart for explaining a routine for determining therequirement of performing the switch control routine according to thepresent invention.

FIG. 4 is a flow chart for explaining the switch control routineaccording to a first embodiment of the present invention.

FIG. 5 is a time chart for illustrating control operations performed bythe method according of the present invention.

FIG. 6 is a flow chart for explaining a switch control routine accordingto a second embodiment of the present invention.

FIG. 7 is a flowchart for explaining a switch control routine accordingto the third embodiment of the present invention.

FIG. 8 is a flow chart for explaining the switch control routineaccording to a fourth embodiment of the present invention.

FIG. 9 is a flow chart for explaining the switch control routineaccording to a fifth embodiment of the present invention.

FIG. 10 shows a schematic illustration of the overall system as amodification of the system of FIG. 1 with a turbocharger system whichincludes an electrically driven boosting device according to the presentinvention to which the method according to the first to fifthembodiments is applicable.

In the following, the structure of the internal combustion engine alongwith associated elements including a turbocharger and the control systemis explained with reference to FIG. 1 and FIG. 2.

As shown in FIG. 1, the structure comprises an internal combustionengine 1 which comprises combustion chambers 3 (four combustion chambersaccording to FIG. 1) each of which is connected to an inlet air line 7and an exhaust line 5. A turbocharger 20 is connected to the internalcombustion engine 1 through said inlet air line 7 and said exhaust line5. In particular, the turbocharger 20 comprises a turbine 15 and acompressor 11 which are mounted on the same shaft. Exhaust gasdischarged from the internal combustion engine 1 through said exhaustline 5 is supplied to the turbine 15 of the turbocharger 20 so as todrive the turbine 15 rotationally. Thereby, the turbine drives thecompressor 11 of the turbocharger 20. The compressor 11 draws air fromthe atmosphere through an air filter 13, compresses said air andsupplies this compressed air via a charge air cooler 9 towards thecombustion chambers 3 through said inlet air line 7.

The internal combustion engine 1 further comprises a fuel supply systemfor supplying fuel to each of the combustion chambers 3 (not shown). Theair introduced to the combustion chambers 3 of the internal combustionengine 1 is mixed with supplied fuel and burned so as to generate powerin a known manner. The exhaust gas which is produced by the combustionis, in turn, passed towards the turbine 15 of the turbocharger 20. Theexhaust gas is directed to an exhaust line 17 so as to discharge thesame to the atmosphere.

The turbocharger 20 further comprises an electric motor 19 which ismounted so as to drive the shaft on which the turbine 15 and thecompressor 11 are mounted. The electric motor 19 is capable of drivingand accelerating the turbocharger including the turbine wheel of theturbine 15 and the compressor wheel of the compressor 11. The electricmotor 19 is supplied by AC electric power by the electric motorcontroller 25. This electric motor controller 25 is connected to thevehicle electrical network 23, which supplies the necessary DC electricpower and to the electronic control unit 21 which send the electricmotor activation command when needed.

Furthermore, the structure comprises an electronic control unit (ECU) 21for controlling the operation of the internal combustion engine 1 and ofthe turbocharger 20 and the like. The electronic control unit 21receives sensor signals from the internal combustion engine and from theturbocharger 20 so as to monitor the operational conditions thereof. Inaddition, the structure comprises a vehicle electrical network 23 whichserves as an electric supply system, as described with reference to FIG.2 below. This vehicle electrical network is linked to the ECU.

The vehicle electrical network 23 according to the present invention isshown in more detail in FIG. 2. The vehicle electrical network 23comprises an alternator 27, a smart switch 29, a battery 31 which servesas an electric energy storage device and an electric boosting system 35which includes the electric motor 19 of the turbocharger 20 and itselectronic controller 25.

The alternator 27 is driven by a mechanic power output from saidinternal combustion engine 1. The alternator 27 generates electricenergy by being driven by the internal combustion engine 1. The electricenergy generated by said alternator 27 is supplied to the vehicleelectrical network 23. The vehicle electrical network 23 includesfurther consumers 33 which consist e.g. in an electric light system L1,further electric motors L2 such as those used for power windows orsunroofs or the like.

The battery 31 is connectable with the alternator 27 such that thealternator is capable of charging the battery. Furthermore, the electricboosting system 35 is connected to the vehicle electrical network 23 andcontrolled by the electronic control unit 21. The electric motor 19 andits associated control electronic (electric motor controller 25) areoperated on a command output from the electronic control unit 21. Theelectric motor controller 25 controls the supply of electric energy tosaid electric motor 19 depending on commands output from the electroniccontrol unit 21 which are based on the operational conditions of theinternal combustion engine 1 and/or the vehicle electrical network 23and the like.

The smart switch 29 is interposed in the connection between thealternator 27 and the battery 31. The smart switch 29 is capable ofdisconnecting the connection between the alternator 27 and the battery31. The electronic control unit 21 is in connection with the smartswitch 29 so as to set said smart switch 29 to an open state or a closedstate depending on the commands output from the electronic control unit21.

A preliminary routine for determining the requirement of operating theelectric booster system applicable to the structure shown in FIG. 1,FIG. 2 and the modification of FIG. 10 is shown in FIG. 3. The flowchart shown in FIG. 3 is a routine which is performed by the electroniccontrol unit 21 in a repeated manner during the operation of the system.

In step S1, the electronic control unit 21 determines, whether theoperation of the electric booster system is required or not. Thisdetermination is based on the operational condition of the internalcombustion engine 1 and of the vehicle electrical network 23. If in stepS1 ‘NO’ is obtained, the switch 29 is set to the closed position in stepS3. Thereby, the connection between the alternator 27 and the battery 31is established. That is, the electric motor 19 of the electric boostersystem 35 can be supplied by electric energy derived from the alternator27 and the battery 31, since both the alternator 27 and the battery 31are connected to the vehicle electrical network 23. Then the routinereturns to the start and is repeated.

If in step S1 ‘YES’ is obtained, the routine proceeds to step S2, inwhich a switch control routine is carried out. The switch controlroutine according to step S2 is shown in the following Figures andexplained in detail below.

The switch control routine is explained based on FIG. 4 according to afirst embodiment of the present invention.

In step S100 the operational state of the internal combustion engine isdetected. That is, the electronic control unit derives sensor signalssuch as rotational speed signals, an accelerator position sensor, andthe like, so as to determine the engine operational state.

In step S104 it is determined, whether a transient condition isestablished or not. That is, the electronic control unit 21 evaluatesthe signals derived from the sensors and judges that the rotationalspeed of the internal combustion engine 1 is required to be accelerated.If such a requirement for an accelerated rotational speed of theinternal combustion engine 1 is judged by the electronic control unit21, it is determined that a transient condition is established so as toobtain ‘YES’ in step S104. In case that the electronic control unit 21does not judge that the requirement of an acceleration of the internalcombustion engine 1 is present, in step S104 ‘NO’ is obtained. If instep 104 ‘NO’ is obtained, the routine proceeds to step S112. In stepS112 the switch is set to the closed position. Thereby, the connectionbetween the alternator 27 and the battery 31 is established.Furthermore, the routine proceeds to ‘RETURN’ so as to start the routineagain.

If in step S104 ‘YES’ is obtained, the routine proceeds to step S106. Instep S106, it is determined, whether the transient condition period isless than a predetermined period or not. If the transient conditionperiod lasts for less than a predetermined period, in step S106 ‘YES’ isobtained. In case that the transient condition period exceeds thepredetermined period, in step S106 ‘NO’ is obtained.

If in step S106 ‘NO’ is obtained, the routine proceeds to step S112. Instep S112 the switch 29 is set to the closed position. Thereby, theconnection between the alternator 27 and the switch 29 is established.Furthermore, the routine proceeds from step S112 to return the routine.If in step S106 ‘YES’ is obtained, the routine proceeds to step S110. Instep S110, the switch is set to the open position. That means, that theconnection between the alternator 27 and the battery 31 is disconnected.The routine proceeds from S110 to return to the start of the routine.

The routine shown in FIG. 4 is repeated in predetermined time intervalsso as to control the position of the switch 29 based on thedetermination of a transient condition in step S104 and based on thetransient condition period in step S106.

According to the basic concept of the present invention, the switch isclosed, if no transient condition is established. If a transientcondition is established, the switch 29 is set to the open position incase that the transient condition period is less than a predeterminedperiod. According to the present embodiment the switch is closed in stepS112 in case where the transient condition period exceeds apredetermined period.

This predetermined period can be freely set. However, the predeterminedperiod according to the present embodiment is 1 second.

The operational behaviour of the electric booster system including theswitch is shown in a time chart in FIG. 5. Section A of FIG. 5 shows theposition of the switch 29 with respect to time. Section B of FIG. 5shows the variable nozzle command output from the electronic controlunit 21 with respect to time. Section C of FIG. 5 shows the electricbooster system motor command with respect to time output from theelectric motor controller 25 based on signals output from the electroniccontrol unit 21.

At a time t0, the switch 29 is closed and the electric booster systemmotor command is switched off. In case where the control methodaccording to the present invention determines that a transient conditionhas established, the electric booster system motor command is switchedon over a ramp as shown in the time period t2 in section C. Furthermore,if the transient condition is determined by the control method accordingto the present invention, the switch is opened over a time period t1shown in section A of FIG. 5. that is, the connection between thealternator 27 and the battery 31 is disconnected over the time periodt1. In this time period t1, the electric energy supplied to the electricmotor 19 of the turbocharger 20 is exclusively supplied by the battery31. After the time period t1 has elapsed, the smart switch is closed ascan be seen in section A of FIG. 5. That means that the connectionbetween the alternator 27 and the battery 31 is reconnected. Therefore,the alternator 27 is capable of supplying electric energy to theelectric booster system 35 and to the battery 31 so as to charge thesame. During the activation of the electric booster system in a timeperiod t2, the variable nozzle command is set to a sufficient value incorrespondence to the requirements of the turbocharger 20 and theinternal combustion engine 1 as can be seen in section B of FIG. 5. Atthe end of the time period t2, shown in section C in FIG. 5, theelectric booster system motor command is decreased by a ramp so as toreach an ‘OFF’ state of the electric booster system at the end of thetime period t2.

The switch control routine according to the second embodiment of thepresent invention is explained based on FIG. 6. The routine shown inFIG. 6 is similar to that shown in FIG. 4, therefore only thedifferences between the routines shown in FIG. 4 and FIG. 6 areexplained.

In the routine shown in FIG. 6, the engine operational state is detectedin step S200 and it is determined in step S204, whether a transientcondition is established or not. If in step S204 ‘NO’ is obtained, theswitch is set to the closed position in step S212. Then, the routinereturns to the start and is repeated.

If in step S204 ‘YES’ is obtained, in step S205 an engine rotationalspeed is detected and the routine proceeds to step S206.

In step S206, it is determined, whether the engine rotational speed isless than a predetermined rotational speed. If the engine rotationalspeed is less than a predetermined rotational speed, in step S206 ‘YES’is obtained. If the engine rotational speed is equal or higher than thepredetermined engine rotational speed, ‘NO’ is obtained in step S206. Ifin step S206 ‘NO’ is obtained, the switch is set to the closed positionin step S212. Then, the routine returns to the start. If in step S206‘YES’ is obtained the switch is set to the open position in step S210.Then the routine returns to the start.

The routine shown in FIG. 6 is repeatedly carried out by the electroniccontrol unit 21.

According to the second embodiment of the present invention as shown inFIG. 6, the engine rotational speed is detected in step S205 and theswitch is set to the open position in step S210 in case that the enginerotational speed is less than a predetermined rotational speed.Therefore, the switch is kept open until the rotational speed of theengine reaches a predetermined rotational speed. Since the alternator 27is driven by the internal combustion engine 1, the rotational speedthereof should be a required rotational speed so as to enable thealternator 27 to output a predetermined electric power. Furthermore, theamount of exhaust gas discharged by the internal combustion engine 1increases along with an increase in the rotational speed in the internalcombustion engine 1. If the rotational speed of the internal combustionengine 1 reaches a predetermined rotational speed, a required amount ofexhaust gas supplied to the turbine 15 of the turbocharger 20 issecured.

As long as the engine rotational speed is less than the predeterminedrotational speed while the transient condition is established, theswitch is kept open according to the present embodiment. If thetransient condition is no longer established or the engine rotationalspeed reaches the predetermined rotational speed, the switch is set tothe closed position.

A third embodiment according to the present invention is explained basedon the routine shown in FIG. 7.

The routine shown in FIG. 7 is similar to that shown in FIG. 4,therefore only the differences between the routines shown in FIG. 4 andFIG. 7 are explained.

In the routine shown in FIG. 7, the engine operational state is detectedin step S300 and it is determined in step S304, whether a transientcondition is established or not. If in step S304 ‘NO’ is obtained, theswitch is set to the closed position in step S312. Then, the routinereturns to the start.

If in step S304 ‘YES’ is obtained, in step S305 an engine rotationalspeed is detected and the routine proceeds to step S306.

In step S306, it is determined, whether the transient condition periodis less than a predetermined period. Furthermore, in step S306, it isdetermined, whether the engine rotational speed is less than apredetermined rotational speed. If the transient condition period isless than a predetermined period and in addition the engine rotationalspeed is less than a predetermined rotational speed, in step S306 ‘YES’is obtained. If one of the conditions of the engine rotational speedbeing equal or higher than the predetermined engine rotational speed andof the transient condition period being equal or longer than thepredetermined period is met, ‘NO’ is obtained in step S306. If in stepS306 ‘NO’ is obtained, the switch is set to the closed position in stepS312. Then, the routine returns to the start. If in step S306 ‘YES’ isobtained, the switch is set to the open position in step S310. Then, theroutine returns to the start and is repeated.

The routine shown in FIG. 7 is repeatedly carried out by the electroniccontrol unit 21.

The third embodiment forms a combination of the first embodiment and thesecond embodiment of the present invention. That is, in step S306 thetransient condition period and the rotational speed are those determinedand the switch is set to the open position in step S310 in case wherethe transient condition period is less than the predetermined periodand, in addition, the engine rotational speed is less than apredetermined rotational speed. If one of the two conditions is not met,the switch is set to the closed position in step S312.

According to the third embodiment, the connection between the alternator27 and the battery 31 is disconnected only in case that the twoconditions according to step S306 are met. If the transient conditionperiod exceeds the predetermined period, the switch is set to the closedposition and the connection between the alternator 27 and the battery 31is reconnected irrespective of the rotational speed with respect to thepredetermined rotational speed. On the other hand, the switch is set tothe closed position in step S312 if the rotational speed exceeds thepredetermined rotational speed irrespective of the transient conditionperiod with respect to the predetermined period.

A fourth embodiment according to the present invention is explainedbased on the routine shown in FIG. 8.

The routine shown in FIG. 8 is similar to that shown in FIG. 4,therefore only the differences between the routines shown in FIG. 4 andFIG. 8 are explained.

In the routine shown in FIG. 8, the engine operational state is detectedin step S400. Then, the routine proceeds to step S410 in which the stateof charge of the battery 31 (SOC) is detected. Then, the routineproceeds to step S402.

In step S402, it is determined, whether the state of charge of thebattery 31 is higher than a predetermined state of charge. If the stateof charge is higher than a predetermined state of charge, ‘YES’ isobtained in step S402. If the state of charge is not higher than thepredetermined state of charge, ‘NO’ is obtained in step S402.

If in step S402 ‘NO’ is obtained, the routine proceeds to step S412where the switch is set to the closed position. Then, the routinereturns to the start and is repeated.

If in step S402 ‘YES’ is obtained, the routine proceeds to step S404. Instep S404, it is determined whether a transient condition is establishedor not. If in step S404 ‘NO’ is obtained, the switch is set to theclosed position in step S412. Then, the routine returns to the start.

If in step S404 ‘YES’ is obtained, the routine proceeds to step S406. Instep S406, it is determined whether the transient condition period isless than a predetermined period or not. If the transient conditionperiod lasts for less than the predetermined period, in step S406 ‘YES’is obtained. In case that the transient condition period exceeds thepredetermined period, in step S406 ‘NO’ is obtained.

If in step S406 ‘NO’ is obtained, the routine proceeds to step S412. Instep S412, the switch 29 is set to the closed position. Furthermore, theroutine proceeds from step S412 to return the routine to the start andto repeat the same.

If in step S406 ‘YES’ is obtained, the routine proceeds to step S410. Instep S410, the switch is set to the open position. Then, the routinereturns to the start and is repeated.

According to the fourth embodiment of the present invention, the stateof charge of the battery 31 is detected and evaluated in the steps S401and S402. Based on the result, the switch is set to the closed positionin case that the state of charge of the battery 31 is not sufficient fordriving the electric booster system 19 exclusively by power derived fromthe battery 31.

On the other hand, if the state of charge of the battery 31 isdetermined to be sufficient for driving the electric booster system 35and, in particular, the electric motor 19 thereof, the switch is set tothe open position so as to supply electric power for driving theelectric motor 19 exclusively by the battery 31.

A fifth embodiment according to the present invention is explained basedon the routine shown in FIG. 9.

The routine shown in FIG. 9 is similar to that shown in FIG. 4,therefore only the differences between the routines shown in FIG. 4 andFIG. 9 are explained.

In the routine shown in FIG. 9, the engine operational state is detectedin step S500 and the routine proceeds to step S501. In step S501, thealternator available power output is monitored. The alternator availablepower output is the difference between the alternator maximum powercapacity and the power consumed by consumers 33 currently connected tothe electrical network. The alternator maximum power capacity can beeasily obtained by a calculation performed by the ECU based on a mapwhich includes e.g. the engine rotational speed versus the maximum poweroutput by the alternator. The current power consumption can be as wellmonitored by the ECU, hence the alternator available power output can bedetermined by the ECU at each time.

Then, the routine proceeds to step S504. In step S504 it is determined,whether a transient condition is established or not. If the transientcondition is established, ‘YES’ is obtained in step S504. If notransient condition is established, ‘NO’ is obtained in step S504.

If in step S504 ‘NO’ is obtained, the routine proceeds to step S512 toset the switch to the closed position. Then, the routine returns to thestart and is repeated. If in step S504 ‘YES’ is obtained, the routineproceeds to step S506.

In step S506, it is determined whether the transient condition period isless than the predetermined period. If the transient condition period isless than the predetermined period, ‘YES’ is obtained in step S506. Ifthe transient condition period is not less than a predetermined period,‘NO’ is obtained in step S506.

If in step S506 ‘NO’ is obtained, the routine proceeds to step S512 toset the switch to the closed position. Then, the routine returns to thestart and is repeated.

If in step S506 ‘Yes’ is obtained, the routine proceeds to step S508. Instep S508 it is determined, whether the alternator available poweroutput is lower than a predetermined value. In particular, thealternator available output is the difference between the calculated ordetected alternator maximum power output capacity and the loadsconnected to the alternator. If the alternator available power output islower than the predetermined value, ‘YES’ is obtained in step S508. Ifthe alternator available output is not lower than the predeterminedvalue, ‘NO’ is obtained in step S508.

If in step S508 ‘NO’ is obtained, the routine proceeds to step S512,where the switch is set to the closed position. Then, the routinereturns to the start and is repeated.

If in step S508 ‘YES’ is obtained, the routine proceeds to step S510. Instep S510, the switch is set to the open position. Then, the routinereturns to the start and is repeated.

According to the fifth embodiment of the present invention, thealternator available power output is considered in the control of theswitch 29. That is, the switch 29 is set to the closed position only ifthe alternator available power output is higher than a predeterminedoutput. Otherwise, the switch is set to the open position.

Thereby, the power supply to the vehicle electric network is secured. Inparticular, if the switch is set to the open position, the battery 31and electric boosting system are disconnected from the rest of thevehicle electrical network 23. Battery and EBS are only reconnected tothe whole vehicle electrical network only when alternator capacity isenough to supply power to EBS and other consumers, avoiding voltage dropduring EBS operation.

The invention is not limited to the above described embodiments andmodifications thereof. In particular, the single structures according tothe above explained embodiments and modifications thereof can be freelycombined with each other.

In particular, the energy storage device 31 can be divided in at leasttwo parts and the connection between only a part of the battery and thealternator 27 is disconnectable by said switch 29.

Furthermore, the vehicle electric network 23 can include a furtherelectric energy storage device which can serve as an auxiliary battery.The connection between the alternator 27 the switch 29 may be such thatthis connection is not disconnectable so as to provide an emergencysystem.

In the following, a modification of the above-described embodiments isexplained. According to the above first to fifth embodiments, theelectrically assisted turbocharger 20 is controlled by performing themethods as shown in FIGS. 3-4 and 6-9. This turbocharger 20, as shown inFIG. 1, comprises a compressor 11 which is driven by an exhaust gasdriven turbine 15 so as to increase the pressure of inlet air fed to theinternal combustion engine 1. However, the method according to the aboveembodiments is also applicable to a boosting device which includes acompressor so as to increase the pressure of the inlet air fed to theinternal combustion engine directly or through a compressor of aturbocharger which is provided in addition to the boosting device.

The structure including a boosting device and a turbocharger is shown indetail in FIG. 10. In the following description, only the differencesbetween the structures shown in FIGS. 1 and 10 are explained.

As shown in FIG. 10, the structure comprises an internal combustionengine 1 which comprises combustion chambers 3 (four combustion chambersaccording to FIG. 10) each of which is connected to an inlet air line 7and an exhaust line 5. A turbocharger 20 a is connected to the internalcombustion engine 1 through said inlet air line 7 and said exhaust line5. In particular, the turbocharger 20 a comprises a turbine 15 and acompressor 11 which are mounted on the same shaft. Exhaust gasdischarged from the internal combustion engine 1 through said exhaustline 5 is supplied to the turbine 15 of the turbocharger 20 a so as todrive the turbine 15 rotationally. Thereby, the turbine drives thecompressor 11 of the turbocharger 20 a.

In addition, a boosting device 40 is provided with a compressor 37 whichis driven by an electric motor 39. The compressor 37 draws air from theatmosphere through an air filter 13, compresses said air and suppliesthis compressed air to the compressor 11 of the turbocharger 20.

Thereby, the pressure of inlet air introduced into the compressor 11 ofthe turbocharger 20 a is boosted before entering the compressor 11.

The boosting device 40 is driven by said electric motor 39 which ismounted so as to drive the shaft on which the compressor 37 is mounted.The electric motor 39 is supplied by AC electric power by the electricmotor controller 25. This electric motor controller 25 is connected tothe vehicle electrical network 23, which supplies the necessary DCelectric power and to the electronic control unit 21 which send theelectric motor activation command when needed.

The main difference between the structure of FIG. 1 and the structure ofFIG. 10 is that the turbocharger 20 a of FIG. 10 is a common devicewhich is not assisted by an electric motor, and that the boosting device40 is provided with the electric motor 39 for boosting the pressure atthe inlet of the turbocharger 20 a in case a transient condition isdetected. The embodiments of the present invention shown in FIGS. 4 and6-9 in addition to the preliminary routine of FIG. 3 are applicable tothe turbocharger system shown in FIG. 10. Then, the electric motor 39 ofthe boosting device 40 of FIG. 10 corresponds to the electric motor 19of the turbocharger system of FIG. 1.

The electric driven boosting device 40 is installed upstream thecompressor 37 of the turbocharger 20 a as shown in FIG. 10. However, theelectric driven boosting device 40 can be installed downstream of theturbocharger 20 a or even downstream of the charge air cooler 9. Theelectric driven boosting device 40 can be even used without theturbocharger 20 a.

In the above-described embodiments, various combinations of parametersare used in the control method. However, the method is not limited tothe parameters as defined in the embodiments. Rather, all engine orvehicle related parameters, such as engine rotational speed, thetransition period, turbocharger rotational speed or various electricquantities such as the state of charge of power output from thealternator can be freely combined in the same method.

1. A method of operating a boosting device comprising a compressor forcompressing inlet air to be supplied to an internal combustion engineand an electric motor for driving said compressor operable by anelectric supply system including an alternator and an electric energystorage device, wherein a connection between said alternator and saidelectric energy storage device is disconnectable, said method comprisingthe following steps: detecting a transient condition wherein saidinternal combustion engine is required to be accelerated, supplyingelectric energy to said electric motor only from said electric energystorage device at the beginning of said transient condition until apredetermined state is reached with said connection being disconnected,supplying electric energy to said electric motor from the electricsupply system after said predetermined state is reached, monitoring astate of charge of said electric energy storage device, and reconnectingsaid connection when said state of charge is smaller than apredetermined state of charge.
 2. A method according to claim 1, whereinsaid predetermined state is reached after the elapse of a predeterminedtime period from the beginning of the transient condition.
 3. A methodaccording to claim 2, wherein said predetermined time period issubstantially 1 second.
 4. A method according to claim 1, wherein arotational speed of said internal combustion engine is detected and saidpredetermined state is a predetermined rotational speed of said internalcombustion engine.
 5. A method as in claim 1, 2, 3 or 4, wherein saidalternator is driven by said internal combustion engine and generateselectric energy for the electric supply system.
 6. A method according toclaim 1, wherein said alternator is capable of charging said electricenergy storage device when said connection is enabled.
 7. A methodaccording to claim 1, wherein a power output value of said alternator ismonitored and said connection is reconnected when said power outputcapacity of said alternator is higher than the demand of said electricmotor and remaining consumer loads derived from the electric supplysystem.
 8. A method according to claim 1, wherein said connection isconnectable and disconnectable by a switch.
 9. A method according toclaim 1, wherein said compressor comprises a variable nozzle, whereinsaid nozzle is adjusted based on the state of said connection.
 10. Amethod according to claim 1, wherein said boosting device furthercomprises an exhaust gas turbine for driving said compressor forming aturbocharger.
 11. A method according to claim 10, wherein said exhaustgas turbine comprises a variable nozzle, wherein said nozzle is adjustedbased on the state of said connection.
 12. A method of operating aboosting device comprising a compressor for compressing inlet air to besupplied to an internal combustion engine and an electric motor fordriving said compressor operable by an electric supply system includingan alternator and an electric energy storage device, wherein aconnection between said alternator and said electric energy storagedevice is disconnectable, said method comprising the following steps:detecting a transient condition wherein said internal combustion engineis required to be accelerated, supplying electric energy to saidelectric motor only from said electric energy storage device at thebeginning of said transient condition until a predetermined state isreached with said connection being disconnected, supplying electricenergy to said electric motor from the electric supply system after saidpredetermined state is reached, monitoring a power output value of saidalternator, and reconnecting said connection when said power outputcapacity of said alternator is higher than the demand of said electricmotor and remaining consumer loads derived from the electric supplysystem.
 13. A method according to claim 12, wherein said connection isconnectable and disconnectable by a switch.
 14. A method according toclaim 12, wherein said compressor comprises a variable nozzle, whereinsaid nozzle is adjusted based on the state of said connection.
 15. Amethod according to claim 12, wherein said boosting device furthercomprises an exhaust gas turbine for driving said compressor forming aturbocharger and wherein said exhaust gas turbine comprises a variablenozzle, wherein said nozzle is adjusted based on the state of saidconnection.
 16. A method of operating a boosting device comprising acompressor for compressing inlet air to be supplied to an internalcombustion engine and an electric motor for driving said compressoroperable by an electric supply system including an alternator and anelectric energy storage device, wherein a connection between saidalternator and said electric energy storage device is disconnectable,and wherein at least one of a variable nozzle of said compressor or avariable nozzle of an exhaust gas turbine of said boosting device isadjusted based on the state of said connection, said method comprisingthe following steps: detecting a transient condition wherein saidinternal combustion engine is required to be accelerated, supplyingelectric energy to said electric motor only from said electric energystorage device at the beginning of said transient condition until apredetermined state is reached with said connection being disconnected,and supplying electric energy to said electric motor from the electricsupply system after said predetermined state is reached.
 17. A methodaccording to claim 16, wherein said connection is connectable anddisconnectable by a switch.